1. Field of the Invention
The present invention relates generally to the field of soybean breeding. In particular, the invention relates to soybean variety 0137335.
2. Description of Related Art
The soybean is an excellent source of protein (Mounts et al., 1987; Fulmer, 1988) and has the potential to supply adequate and nutritious food and feed for use by ever-increasing world production. Current soybean cultivars average approximately 41% protein and 21% oil in the seed on a dry weight basis (Leffel and Rhodes, 1993).
Most commercially produced soybeans are processed to produce edible oil and one or more protein products. The initial protein fraction is a soybean meal, either containing the fiber from the seed hull (44% protein soymeal) or separated from the hull fiber (48.5% protein soymeal). The initial meal fraction is often further processed to produce more highly refined protein products, primarily soy protein concentrate or soy protein isolate. In any of these protein fractions—meal, concentrate or isolate—the protein component is of economic or nutritional value. Soy protein is valued for its high nutritional quality for people and livestock, and for functional properties, such as gel and foam formation. Alternative processing methods produce protein-based soy foods, such as tofu or soymilk. With the economic value of soy protein, soybeans with higher concentration of protein are very desirable. However, higher protein content cannot be associated with lower oil content or lower seed yield per acre if an economic benefit is to be obtained.
Breeding programs for increased protein content of soybean seed have been in progress for many years (Burton, J. W. 1985; Hartwig, E. E. 1969; Hartwig, E. E. 1979; Johnson, H. W. 1961; and Leffel, R. C. 1988). However, with a few exceptions, high protein soybeans developed to date have not been as high in yield as commercial cultivars. Studies have shown negative genetic correlations between soybean seed yield and protein content (Caldwell et al., 1966; Hinson et al. 1972; Kwon and Torrie, 1964; Thorne and Fehr, 1970; Burton, 1988; Leffel and Rhodes, 1993; Serretti et al., 1994; Pantalone et al., 1996; Simpson and Wilcox, 1983: Shannon et al. 1972). The high negative correlation between the traits lead Hartwig (1973) to conclude that it is not possible to retain high oil along with high protein content. Openshaw and Hadley (1984) concluded that breeding methods designed to increase both protein and oil showed limited success. Orf (1988) concluded that producing soybean varieties with high protein, high oil, and high yield will be difficult from a breeding standpoint and may not be a realistic conventional breeding objective. Hymowitz (1976) indicated that it is probable that lower protein soybeans will be caused in the long term if an emphasis is maintained on the yield of soybeans.
The negative association has a strong genetic basis (tight linkages, pleiotropy, or both), and selection for percent protein should result in reduced yield. Studies of selection indices involving both yield and percent protein have generally confirmed the negative relationship. Caldwell et al.(1966) predicted a yield decrease when percent protein was the sole selection criterion. Burton (1984) summarized the results of several breeding studies, reporting genotypic correlations between seed yield and seed protein percentage varying from −0.12 to −0.74. In only one population was there a positive genotypic correlation between these two traits. Additional studies by Sebern and Lambert (1984), Simpson and Wilcox (1983), and Wehrmann et al. (1987) reported moderate to strong inverse relationships between seed yield and seed protein with correlation coefficients ranging from −0.23 to −0.86.
In the past, the pedigree and backcrossing methods have been used with limited success to select soybean lines with high percent protein. Cianzio and Fehr (1982) evaluated seed protein and oil of F2-derived lines in the F2 generation and BC1F1-derived and BC2F1-derived lines in the F3 generation of crosses between the high protein lines Pando and PI 153.269 and the high yielding cultivars Wells and Woodworth. No line from either set of crosses had protein concentration as high as those of the high protein donor parent. Mean protein percentages and genetic variances of the populations decreased with each backcross to the high yielding parent. The results indicated to them that it will be difficult to transfer genes for extremely high protein levels to cultivars with lower protein. No yield data were recorded on the breeding lines evaluated in this study.
Wehrmann et al.(1987) evaluated 95 BC2 progenies in each of three populations, where the recurrent parents were high yielding lines and the donor parent was Pando, that averaged 480 g kg−1 seed protein. In these populations, no backcross-derived lines were recovered that combined exceptionally high seed protein with the yield of the recurrent parent. In each of two populations, the highest protein line averaged only 422 and 433 g kg−1 protein and did not differ significantly in yield or seed oil from the recurrent parent. In the third population, the highest protein line averaged 462 g kg−1 protein but was significantly lower in both yield and seed oil concentration than the recurrent parent.
There have been isolated reports that genotypic correlations between seed yield and seed protein percentage may not be as strong as the literature has indicated (Byth et al. 1969; Wilcox and Cavins, 1995). However, none of the backcross studies evaluated progenies beyond the BC3 generation. The lack of success in transferring exceptionally high seed protein to high yielding cultivars by backcrossing has cast doubt on the possibility of combining these two traits in adapted germplasm or cultivars.
All crop species are grown for the purpose of harvesting some product of commercial significance. Enhancement of productivity or yield of that product is a major goal of most plant breeding programs. The highest priority in most soybean cultivar development programs is increasing seed yield. Seed yield is a quantitative character controlled by many genes and strongly influenced by the environment. The heritability of yield is the lowest and the most variable of the major agronomic traits considered in cultivar development, with heritability estimates ranging from 3 to 58%. Yield is an example of a quantitative character that breeders attempt to improve beyond the level of that present in current cultivars. Disease resistance is required in most cases to protect the yield potential of a cultivar.
It is a difficult challenge to incorporate increased protein or oil content into high yielding cultivars given the negative correlations observed among the traits. The difficulty of obtaining a commercially acceptable variety is increased several fold if a breeder attempts to significantly increase total protein without a loss in oil content into one cultivar. Perhaps because of these difficulties, the prior art has failed to provide high yielding soybean varieties that posses high seed protein without decreased seed oil. However, there is a great need in the art for such soybean plants. Increased seed protein can significantly improve the value of a soybean harvest. For the increase in seed protein to have commercial significance, yield and/or oil content must not be substantially impacted. Therefore, providing soybean plants that are both high yielding and posses high combined protein and oil would represent a substantial advance in the art and benefit farmers and consumers alike.